En español l As important as the emergency room is in the nation's health care system, consumers know very little about how medical charges are calculated or the size of the bills they face, according to a study by a team of researchers at the University of California, San Francisco.

Reduce the risk of sticker shock after an emergency room visit: Ask for an itemized bill. — Alex Nabaum

"There's no blue book for health care costs," says senior author Renee Hsia, M.D., whose team studied 8,303 emergency room visits by adults 18 to 64 from 2006 to 2008. The study, published in the journal PLOS ONE, spotlighted the 10 most common outpatient conditions (ranging from pregnancy to open wounds) and found giant price differences. Here, a few examples:

Causes for the disparity in charges were not examined, though earlier studies cited by the authors highlighted location and differences in reimbursement methods. Uninsured patients were charged the lowest median price ($1,178), followed by those with private insurance ($1,245) and Medicaid ($1,305).

While patients with true emergencies such as heart attacks and strokes have little choice, there are occasions when patients can reduce the risk of financial surprise by asking questions. Hsia's advice if you must pay for an ER visit: Always ask for an itemized bill. And if you try to negotiate the costs, you might just succeed.